Field
This invention relates generally to a field effect transistor (FET) device that includes a hydrogen inhibitor for preventing hydrogen poison induced degradation (HPID) of the device and, more particularly, to an FET device provided within a hermetically sealed package, where the FET device includes a hydrogen inhibitor that replaces platinum in a gate metal of the device, and where the hydrogen inhibitor prevents hydrogen gas from forming hydrogen atoms so as to eliminate HPID.
Discussion
It is known in the art to provide hermetically-sealed packages for integrated circuits, such as monolithic millimeter-wave integrated circuits (MMIC). One or more MMICs are fabricated on a semiconductor substrate, and mounted within a metal housing. A metal cover is then sealed to the housing in a vacuum environment to provide the hermetically-sealed package. These types of hermetically sealed MMICs have many applications, such as space-based applications, where device reliability is crucial.
MMICs that are contained with hermetically sealed packages usually include one or more FET devices, such as high electron mobility transistors (HEMT). A typical gate metal for the gate terminal of an FET device includes stacked layers of titanium (Ti), platinum (Pt) and gold (Au), where the gate terminal is covered with a silicon nitride passivation layer. In these types of packages, hydrogen gas H2 is out-gassed from the hermetic package and is contained therein. It is believed that the hydrogen gas H2 diffuses through the silicon nitride passivation layer and adsorbs on the surface of the platinum layer, which is catalyzed and dissociates into hydrogen atoms H. The hydrogen atoms H combine with the titanium in the gate metal to form TiHx, which reduces the device gate voltage Vg and decreases the device transconductance Gm, thus affecting device performance.
In order to alleviate hydrogen caused degradation of integrated circuit components within hermetically-sealed packages, sometimes referred to as hydrogen poison induced degradation (HPID), it has been proposed in the art to provide hydrogen getters within the package that absorb the hydrogen gas H2 to remove it from the sealed package. Particularly, it is known in the art to deposit certain layers of material within the hermetically-sealed package that operate to absorb the hydrogen gas H2 that may otherwise degrade device performance. For example, a hydrogen getter can be mounted to the cover of the hermetically sealed package discussed above. One known hydrogen getter includes a plurality of metal layers deposited on either the substrate wafer or the cover wafer, and may include titanium layers, nickel layers and palladium layers.
Although hydrogen getters have been effective for reducing or eliminating HPID in an FET device, fabricating the hydrogen getter in the sealed package increases the manufacturing cycle time of the integrated circuit including the FET device, which also increases cost. Further, hydrogen getters are not always reliable as they often degrade and/or malfunction before the end of the life of the FET device.